The invention is concerned with a device for protecting motor-vehicle wheels against theft which device comprises a freely rotatable sleeve covering the polygonal head of a wheel nut or screw. A cylinder lock, which is provided with at least one tumbler entering the inner wall of a cylinder lock location cavity of the polygonal head which projects beyond the circumference of the cylinder lock, engages rotatably into the sleeve. In the position for preventing theft, the tumbler engages behind a lock shoulder of the polygonal head.
Devices of this general type are known from EP-PS No. 0,039,855. The locking shoulder acting together with the tumbler is formed in the devices described in the European Patent by the one steep flank of an annular groove. According to the number of tumblers, a row of annular grooves lying closely one behind one another is provided. Because the recessing of the grooves is carried out from the relatively small location cavity it is difficult from the point of view of manufacture, even without taking into account the relatively tough material of such wheel nuts or screws. The narrow width of the groove is also frequently the cause of clogging of the turnings. It requires careful final inspection. The edge life of the turning tool is very short, which makes the manufacturing process more expensive.
It is also known from DE-OS No. 3,520,452 to abandon the direct engagement between tumbler and inner wall of the cylinder lock location cavity of the polygonal head and to guide in the engagement direction a spring-loaded locking member, which acts together with a radial locking shoulder of the polygonal head. The latch-like locking member, provided in pairs, yields when assigned to the sleeve in order then to spring latch-like into the locking position. By inserting a suitable key the locking member is moved out of the locking position by the tumblers, so that the rotary cylinder can then be withdrawn. Such a design is however expensive to manufacture and assemble.